Caffeine monitoring in biological fluids and dietary supplements by solid surface fluorescence using rhodamine and nanotubes modified membranes

Abstract

Background: In thiswork, a newmethodology based upon enhancement of rhodamine B fluorescent signal is pro- 24 posed for the quantification of caffeine traces. 25 Methods:Membrane filters treated withmultiple wall carbon nanotubeswere employed as solid support for de- 26 termination step by solid surface fluorescence. 27 Results: Experimental variables that influence the preconcentration step and fluorimetric sensitivity have been 28 optimized using uni-variation assays, presenting linearity from 1.1 to 9.7 × 103 μg/l, with a correlation coeffi- 29 cient of 0.99. At optimal conditions, a limit of detection of 0.3 μg/l and a limit of quantification of 1.1 μg/l were 30 obtained. Themethod showed good sensitivity and adequate selectivity and was satisfactorily applied to the de- 31 Q5 termination of trace amounts of caffeine in urine, plasma and serumbelonging to subjectswith different sex, ages 32 and habit of caffeine intake. 33 Conclusions: Chemofiltration step eliminated the highly fluorescentmatrix, thus enabling and allowing CF quan- 34 Q6 tification, in the presence of other methylxanthines. The proposed methodology represents an innovative appli- 35 cation of the solid surface fluorescence using membrane filters modified with MWCNTs.